To form a person or animal, the many cells that form the body have to work together and play their assigned roles during development. This image shows a signal that is present in a defined set of cells. This signal tells those cells play a different role than their neighbors without the signal. In this case, the signal makes cells change shape together, which changes the shape of the whole organism
This image shows the sharp boundary between two types of tissues (marked by the transcription factor snail in cyan), one in which cells drastically change shape vs one in which they won’t. I took this image to show how the pattern set up by snail creates a pattern of cell junctions (magenta) that we believe is important for successful tissue shape change.